Background: Chemokine receptor CCR7 promotes survival in mature dendritic cells (mDCs). Results: Activated AMP-dependent kinase (AMPK) induces apoptosis in mDCs; CCR7 uses the kinases MEK1/2-ERK1/2 to regulate phosphorylation of AMPK on Ser-485 and consequently its inhibition. Conclusion: CCR7 uses a novel MEK1/2-ERK1/2-AMPK signaling axis to induce survival in mDCs. Significance: AMPK is a potential target to regulate mDC-mediated immune responses.

Summary Loss of pigment epithelium-derived factor (PEDF, SERPINF1) in cancer cells is associated with poor prognosis and metastasis, but the contribution of stromal PEDF to cancer evolution is poorly understood. Therefore, we investigated the role of fibroblast-derived PEDF in melanoma progression. We demonstrate that normal dermal fibroblasts expressing high PEDF levels attenuated melanoma growth and angiogenesis in vivo, whereas PEDF-depleted fibroblasts exerted tumor-promoting effects. Accordingly, mice with global PEDF knockout were more susceptible to melanoma metastasis. We also demonstrate that normal fibroblasts in close contact with PEDF-null melanoma cells lost PEDF expression and tumor suppressive properties. Further mechanistic investigations underlying the crosstalk between tumor and stromal cells revealed that melanoma cells produced PDGF-BB and TGF-β, which blocked PEDF production in fibroblasts. Notably, cancer-associated fibroblasts (CAF) isolated from patient-derived tumors expressed markedly low levels of PEDF. Treatment of patient CAF and TGF-β-treated normal fibroblasts with exogenous PEDF decreased the expression of CAF markers and restored PEDF expression. Finally, expression profiling of PEDF-depleted fibroblasts revealed induction of interleukin-8, SERPINB2, hyaluronan synthase-2, and other genes associated with tumor promotion and metastasis. Collectively, our results demonstrate that PEDF maintains tumor-suppressive functions in fibroblasts to prevent CAF conversion, and illustrate the mechanisms by which melanoma cells silence stromal PEDF to promote malignancy.